This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Glutamate excitotoxicity is an important mediator of neuronal cell death and may contribute to the pathology of stroke, epilepsy and traumatic brain injury. The chief mechanism of neuronal injury during prolonged glutamate exposure is due to Ca2+ entry through NMDA glutamate receptors and consequent sequestration of Ca2+ by mitochondria. This leads to mitochondrial Ca2+ overload, increase in ROS production, disruption of bioenergetics and loss of cellular architecture. Alternative theories suggest that accumulation of Ca2+ and indeed Na+ may lead to an increase in ATP demand from ATP-consuming pumps and consequent depletion of intracellular ATP. It remains a question whether ATP depleting conditions are a determinant or a manifestation of cell death. In conjunction with the Mattson Laboratory (NIA), the BRC has aimed to assess oxygen consumption in single hippocampal neurons in order to gain insight into mitochondrial respiratory capacity during exposure to glutamate. Maximal oxygen consumption is a good indicator of critical ATP depletion, as observed during exposure to mitochondrial uncoupler compounds. Oxygen consumption has only been assessed in whole neuronal populations prior to this proposal. This leads to problems such as the time responsiveness to drugs as well as the need for a homogeneous population of cells. With the development of self-referencing oxygen microsensors, the BRC is able to measure oxygen flux and therefore oxygen consumption at the single cell level. By combining this technique with confocal microscopy, it is anticipated that temporal relationships between mitochondrial membrane potential, intracellular Ca2+ and oxygen consumption will be established and provide clues to the underlying mechanism of excitotoxicity.